1. Field of the Invention
The present invention relates to an orthodontic bracket, and more particularly to an orthodontic bracket having a shiftable locking member so as to open or close an arch wire slot in a bracket body as well as a tool for an orthodontic bracket.
2. Description of the Related Art
As is known, orthodontic treatment is effected by fixing small appliances called orthodontic brackets to a patient""s teeth. Namely, the orthodontic brackets are most commonly used by being fixed to the patient""s teeth in an appropriate manner so as to correct the misaligned teeth by applying an external force thereto through an arch wire extending between the fixed orthodontic brackets.
As to the structure of these orthodontic brackets, they are constructed of a body having small slots and are adhered directly on the labial or lingual sides of the teeth or welded to such as metal bands attached to the teeth by cementing or by some other method.
As the form of use of the orthodontic bracket constructed as described above, an elastic arch wire, which is curved so as to conform to a dental arch, is placed in a slot in the bracket, and the tooth can be shifted over time by the restoring force of the elastic arch wire so that the teeth become well aligned.
Namely, with the orthodontic bracket, a force can be applied to the tooth in a desired direction (in the direction in which the tooth is shifted, rotated, or tilted) by the three-dimensional inclination of the slot formed in the bracket body or by the desired bending of the arch wire.
The conventional orthodontic bracket has tie wings, and a ligature wire or an elastomeric ligature ring is hooked on the tie wings so as to positively hold the arch wire to prevent the arch wire from coming out of the slot in the bracket. The dentition that should be treated is of malocclusion, in which the arch wires are greatly deformed when engaged. Orthodontic treatment is done by transmitting the restoring force of the arch wires through brackets to the tooth roots. Generally, in an early period of the treatment, a thin soft round wire is used, and an operation is required to loosen the ligature wire after ligating it such that the round wire freely slides within the slot (on a nonfrictional basis). In addition, the frictional force cannot be eliminated with the elastomeric ligature ring.
As treatment progresses, a thicker wire, a square wire, and a more highly rigid wire come to be used. When the shifting treatment is nearly completed, they are held for a while to prevent relapsing. At this time, there are cases where the tooth is strongly fastened by a ligature wire so that it practically does not shift.
In the orthodontic treatment as described above, different arch wires of many varieties are used in succession during the course of the treatment. During patient visits to the clinic, it is necessary to remove the ligature wire and adjust the bend of the arch wire or replace it. This operation requires much chair time and imparts discomfort to the patients.
In addition, an end of the ligature wire which has been cut after ligation is accommodated so as to be bent and thrust into a groove under the tie wing. Such modes of attachment lead to problems of food residues tending to adhere. As a result, comparatively large number of measures had to be taken in order to maintain good hygienic conditions inside the teeth. In addition, there are cases where the ligature wire causes the trouble of imparting stimuli to the soft tissue of the patient""s tongue or cheek as its bent end becomes exposed from below the tie wing. If this ligature wire is cut and reshifted, the patient may swallow the dislocated ligature wire, or the treatment may make no progress. Further, in recent years serious concern has been expressed over various infectious diseases which occur due to bleeding caused by the piercing of the doctor""s fingers by the ligature wire.
The various problems due to the use of such a ligature wire can be overcome to some extent by using a lock-type orthodontic bracket. Namely, this lock-type orthodontic bracket has the structure which does not require the tie wire for ligation, and has a locking member incorporated in the bracket and capable of shifting for opening or closing the slot in the bracket. As the locking members, there are, for example, rotating-type and sliding-type locking members. Since the locking members are capable of shifting, the retention of the arch wire in the slot or disengagement of the arch wire from the slot can be effected very easily. In addition, the structure is free of a bent portion of the ligature wire and is therefore trim, it is easy to avoid such as the sticking of food and its residue.
As shown in FIG. 13, with the orthodontic bracket having the aforementioned sliding-type locking member, an arch wire 50 in an arch wire slot 85 provided in a bracket body 82 is locked in the slot by a tip portion of a locking member 120 mounted on the bracket body 82. As for the tip portion of the locking member 120, its shift in the loosening direction is restricted by a stop groove 86 continuing to the slot 85, for example. Normally, the arch wire 50 in the slot 85 is located on the bottom side of the slot, as shown in FIG. 13. However, when an unexpected large external force is applied to the arch wire 50, the arch wire 50 can enter the stop groove 86 and become caught therein, as shown in FIG. 14.
In such a state, the arch wire 50 fails to shift smoothly inside the slot, and a hindrance is caused to the orthodontic treatment. To avoid such a state, it is conceivable to decrease the width W of the stop groove 86, but if that width W is decreased, the function of the locking member 120 (the function of pressing down the wires ranging from the narrow round wire to the full-size square wire within the range of the elasticity) declines, so that it is not desirable to do so.
In addition, there has been a problem in that when an unexpected large external force is applied to the arch wire 50, a tip portion 121 of the locking member 120 becomes twisted as the arch wire 50 is twisted, thereby rendering the wire retention unstable. In the structure disclosed in U.S. Pat. No. 5,906,486, an arrangement is shown in which the position of the tip portion of the locking member is restricted in such a manner as to close both ends of the stop groove. In such a structure, however, since the arrangement is provided so as to close both ends of the stop groove, the width of the tip portion of the locking member must be inevitably made smaller than the length of the slot. Accordingly, there has been a drawback in that the tip portion of the locking member has insufficient rotation control since its length for holding the arch wire is short.
The invention has been made to overcome the above-described problems, and its object is to provide an orthodontic bracket having a locking member which makes it possible to avoid the situation of the arch wire becoming coming out the slot and entering the stop groove, and which makes the retention of the arch wire more reliable and excels in the operating efficiency. In the orthodontic brackets of rhomboid-type and torque-in-base type orthodontic brackets, the object is to provide an orthodontic bracket excelling in the handling efficiency. Another object of the invention is to provide a tool excelling in the efficiency in handling the locking member.
In accordance with the invention, there is provided an orthodontic bracket including a base secured to a tooth surface, a bracket body extending in a substantially perpendicular direction from the base, an arch wire slot which extends in a mesiodistal direction substantially in a center of the bracket body and is open in the front, and a locking member capable of opening or closing the arch wire slot, wherein the locking member is structured in a substantially U-shaped cross-sectional configuration, one side thereof being formed as a base side portion located on a base side and extending along the base, another side thereof being formed as a counter base side portion having substantially the same width as the length of the arch wire slot and extending on an upper side of the slot, the locking member being formed of an elastic member in which a notched portion is provided substantially in a center of the counter base side portion, and that the bracket body has a closing stop groove formed at an open edge portion of the arch wire slot so as to stop a tip of the locking member in a slot closed position as well as an open stop concavity formed at an edge portion thereof located away from the stop groove so as to stop the tip of the locking member in a slot open position, a rib being formed in a longitudinally central portion of the stop groove in such a manner as to project so as to bury the stop groove in correspondence with the notched portion. Consequently, the above object can be attained.
The orthodontic bracket in accordance with the invention preferably has the following features.
The bracket body is a twin bracket having a central groove sandwiched between mesial tie wings and distal tie wings, and the rib is formed over an entire width of the central groove and is formed in such a manner as to be connected to the mesial tie wing and the distal tie wing.
The bracket body is a single bracket having a tie wing.
The bracket body is a lingual bracket which is mounted on a lingual side of a tooth.
A recessed portion is formed in an upper end surface of the rib.
An engaging end portion formed by a recess or a notch is formed at a rear end portion of the base side portion of the locking member.
The bracket body has an opening extending therethrough along the mesiodistal direction.
The bracket body has a projection provided on a side surface of the tie wing where an edge portion of the locking member slides, the projection being capable of abutting against the edge portion, the projection being arranged to be located on an outer side of the edge portion when the slot is closed by the locking member.
The bracket body is provided with a hook rising and jetting out in the mesiodistal direction of the tie wing of the bracket body.
The locking member is formed of a single plate material, and is structured such that a portion of the base side portion located close to the base with a substantially longitudinally central portion as a boundary is set at an angle of inclination conforming to the angulation of the bracket, while the counter base side portion on an opposite side away from the side close to the base is set at an angle of inclination which is obtained by correcting an angle corresponding to a bent portion for pressing the arch wire in addition to the angle of inclination of the bracket angulation, a curved portion connecting the base side portion and the counter base side portion forming a portion of a sine curve.
The bracket body has a rhomboid-type shape, and wherein mesial and distal edge portions of the counter base side portion of the locking member and mesial and distal edge portions of the base side portion, in a top view of the bracket, are formed in parallel along mesial and distal ends of the tie wing of the bracket, and edge portions of the counter base portion extending along the mesiodistal direction are formed to be parallel to the arch wire slot.
The bracket body has a non-rhomboid-type shape and is of a cut-angulation- type in which, in a plan view of the bracket body, the arch wire slot is inclined with respect to a straight line of the edge portion of the bracket body, and edge portions of the counter base side portion of the locking member extending in the mesiodistal direction are formed to be parallel to the arch wire slot.
The locking member is formed of a superelastic member.
The locking member is formed of a beta titanium alloy.
The locking member is formed of a cobalt-nickel-base alloy (Coxe2x80x94Ni-base alloy) containing chromium (Cr) and molybdenum (Mo).
The locking member is formed of a work-hardening nickel-titanium (Nixe2x80x94Ti) alloy.
The bracket body has a torque-in-base structure, and the base side portion of the locking member is formed so as to be located in parallel to the base inclined in correspondence with torque.
The base side portion of the locking member is arranged to slide over the base.
A tool for an orthodontic bracket in accordance with the invention is characterized by comprising: a fulcrum portion engageable with a portion of the bracket body and an acting portion engageable with a rear end portion of the base side portion, wherein the locking member is operated to slide by using the portion of the bracket body as a fulcrum and an engaging end portion of the rear end portion as a point of application. Consequently, it is possible to attain the above object.
In the tool for an orthodontic bracket in accordance with the invention, the fulcrum portion is arranged to be engageable with a recessed portion in an upper end surface of the rib.
In accordance with the orthodontic bracket pertaining to the invention, the locking member is structured in a substantially U-shaped cross-sectional configuration, one side thereof being formed as the base side portion located on the base side and extending along the base, another side thereof being formed as the counter base side portion having substantially the same width as the length of the arch wire slot and extending on the upper side of the slot, the locking member being formed of an elastic member in which the notched portion is provided substantially in the center of the counter base side portion. The bracket body has the closing stop groove formed at an open edge portion of the arch wire slot so as to stop a tip of the locking member in a slot closed position as well as the open stop concavity formed at an edge portion thereof located away from the stop groove so as to stop the tip of the locking member in a slot open position. By virtue of this arrangement, the locking member is capable of sliding on the bracket body so as to open or close the arch wire slot.
In addition, since the rib is formed in a longitudinally central portion of the stop groove in such a manner as to project so as to bury the stop groove in correspondence with the notched portion of the locking member, it is possible to avoid a situation in which the arch wire is disengaged from the slot and enters the stop groove. Further, since the notched portion of the locking member is correspondingly provided for the rib in the stop groove so as to be fitted to it, the shift and twisting of the tip portion of the locking member in the longitudinal direction of the slot can be effectively suppressed. Namely, with respect to the shift and twisting of the tip portion of the locking member in the longitudinal direction of the slot, such shift can be suppressed by the rib provided in a central region of the stop groove. Moreover, the distance for holding in the mesiodistal direction of the tip of the locking member can be made large without being restricted by the structure of the bracket body.
In addition, in the above-described orthodontic bracket in accordance with the invention, according to the arrangement in which the bracket body is a twin bracket having a central groove sandwiched between mesial tie wings and distal tie wings, and the rib is formed over the entire width of the central groove and is formed in such a manner as to be connected to the mesial tie wing and the distal tie wing, the bracket body can be reinforced by this rib.
In addition, in the above-described orthodontic bracket in accordance with the invention, if the bracket body is a single bracket having tie wings, it is possible to provide an orthodontic bracket which has a locking member and can be used for a rotated tooth or lower jaw anterior teeth having a narrow tooth width and which excels in mountability and operating efficiency.
In addition, in the above-described orthodontic bracket in accordance with the invention, if the bracket body is a lingual bracket which is mounted on a lingual side of a tooth, it is possible to provide an orthodontic bracket which has a locking member and can be used for the lingual side of the tooth for which ligation with a ligature wire is difficult and which excels in mountability and operating efficiency.
In addition, in the above-described orthodontic bracket in accordance with the invention, according to the arrangement in which a recessed portion is formed in an upper end surface of the rib, it is possible to insert a tool or the like into the recessed portion, and the recessed portion can be used at the time when the bracket body or the locking member is operated. Further, in a case where the recessed portion has, for instance, a triangular shape, it is effective for the doctor to discriminate the upper and lower sides in the axial direction of the tooth.
In addition, in the above-described orthodontic bracket in accordance with the invention, since an engaging end portion formed by a recess or a notch is formed at a rear end portion of the base side portion, the tool can be engaged in this notch or the recessed portion, and the doctor is able to easily release the locking member by operating the tool with his or her finger without directly viewing this engaging end portion.
In addition, in the above-described orthodontic bracket in accordance with the invention, since the bracket body has an opening extending therethrough along the mesiodistal direction, by making use of this opening, treatment can be effectively advanced by attaching an appropriate means for fixing the locking member, by retracting anterior teeth portion by passing an auxiliary wire therethrough, or by using an auxiliary means such as an uprighting spring, a rotation spring, or the like.
In addition, in the above-described orthodontic bracket in accordance with the invention, an arrangement is provided such that the bracket body has a projection provided on a side surface of the tie wing where an edge portion of the locking member slides, the projection being capable of abutting against the edge portion, the projection being arranged to be located on an outer side of the edge portion when the slot is closed by the locking member. Accordingly, when an unexpected external force has been applied in the oral cavity, this projection holds down a portion of the locking member (a curved portion of the locking member), so that an unintentional release of the locking member can be avoided. In addition, when an attempt is made to manipulate the U-shaped curved portion of the locking member by pressing it so as to close the slot, the clicking pressure can be felt by the finger when this projection is ridden over, so that it is possible to confirm the closure of the slot.
In the above-described orthodontic bracket in accordance with the invention, since the bracket body is provided with a hook rising and jetting out in the mesiodistal direction of the tie wing of the bracket body, when the tool is engaged with the bracket body, since the hook juts out so as to escape laterally from the bracket body, no hindrance is caused to the operating efficiency.
In the above-described orthodontic bracket in accordance with the invention, according to the arrangement in which the locking member is formed of a single plate material, the locking member can be fabricated very easily by such as blanking a plate material. In addition, the arrangement provided is such that a portion of the base side portion located close to the base by using as a boundary a substantially longitudinally central portion of the portion (leg) extending toward the base side portion in the locking member is set at an angle of inclination conforming to the angulation of the bracket, while the counter base side portion on an opposite side away from the side close to the base is set at an angle of inclination which is obtained by correcting an angle corresponding to a bent portion for pressing the arch wire in addition to the angle of inclination of the bracket angulation, a curved portion connecting the base side portion and the counter base side portion forming a portion of a sine curve. Accordingly, in a top view of the locking member, the left and right edge portions of the counter base side portion can be formed to be seen as straight lines. Hence, in the case where the shape of the bracket body is of the rhomboid type, the line of each edge portion of the counter base side portion can be utilized in the alignment of the bracket.
In the above-described orthodontic bracket in accordance with the invention, the arrangement provided is such that the bracket body has a rhomboid-type shape, and wherein mesial and distal edge portions of the counter base side portion of the locking member and mesial and distal edge portions of the base side portion, in a top view of the bracket, are formed in parallel along mesial and distal ends of the tie wing of the bracket, and occlusal edge portions (edge portions close to the base side portion) of the counter base portion and a gingival side edge portion of the notched portion (an edge portion at an innermost portion of the notch) are formed to be parallel to the arch wire slot. Accordingly, in a top view of the bracket, these edge portions are parallel to the respective sides of a parallelogram of the bracket, so that the respective edge portions of the locking member in the mesiodistal direction and in the axial direction of the tooth can be utilized in the alignment of the bracket.
In the above-described orthodontic bracket in accordance with the invention, the arrangement provided is such that the bracket body is of a cut angulation type in which the arch wire slot is inclined with respect to a contour line of a square (non-rhomboid) bracket, and edge portions (tip edge portions, occlusal-side edge portions, and the gingival-side edge portion in the notched portion) of the counter base side portion of the locking member extending in the mesiodistal direction are formed to be parallel to the arch wire slot. Accordingly, in the orthodontic bracket of the cut angulation type, the respective edge portions of the locking member can be utilized in the alignment and orientation.
In the orthodontic bracket in accordance with the invention, since the locking member is formed of a superelastic member, i.e., a member having a state in which even if the amount of deformation has increased more than a specific amount, the change in load does not increase and is maintained at a substantially fixed level. Therefore, even if the locking member has undergone relatively large deformation, there is no major change in the load, and it is possible to maintain favorable operating efficiency in the moderate holding down of the arch wire and in the treatment operation.
In addition, in the orthodontic bracket in accordance with the invention, if the locking member is formed of a beta xe2x80xa2 titanium alloy, since it is possible to enlarge the pressing force (load) relative to the amount of deformation, the slot can be sealed reliably and the arch wire can be pressed positively.
Further, in the orthodontic bracket in accordance with the invention, if the locking member is formed of a cobalt-nickel-base alloy (Coxe2x80x94Ni-base alloy) containing chromium (Cr) and molybdenum (Mo), e.g., Elgiloy (trade name) manufactured by Elgin Inc. of the United States or SPRON (trade name) of SII Micro Parts Inc., since relatively large amounts of chromium and molybdenum are contained, such an alloy is able to exhibit high fatigue resistance and corrosion resistance although it has an excellent spring characteristic.
In addition, in the orthodontic bracket in accordance with the invention, if the locking member is formed of a work-hardening nickel-titanium (Nixe2x80x94Ti) alloy, since the elastic limit in the case of this alloy is also high, the slot can be sealed reliably and the arch wire can be pressed positively.
In addition, in the orthodontic bracket in accordance with the invention, if the bracket body has a torque-in-base structure, the pressing direction of the counter base side portion of the locking member with respect to the arch wire can be substantially set in a fixed manner. Accordingly, since the arch wire can be maintained in the slot with the orientation and magnitude of a stable pressing force, an effect of accurate treatment can be expected. Namely, even in a case where a plurality of bracket bodies of different forms are used, since the relationship between the arch wire and the locking member can be fixed in any case, it is easy to estimate the treatment effect, and a positive effect of treatment can be expected. In addition, since the arrangement provided is such that the base side portion of the locking member is formed so as to be located in parallel to the base inclined in correspondence with torque, and is located close to the bonding base in any case of the torque, the tip portion of the base side portion is not located so as to block the space below the tie wings, so that the amount of food residue stuck can be reduced.
In addition, since the base side portion of the locking member is arranged to slide over the base, the base side portion at any position is held by the base. For example, even in a case where the operation of strongly pressing its rear end by a tool is effected, the base side portion is able to open stably without becoming deformed.
The tool for an orthodontic bracket in accordance with the invention is characterized by comprising: a fulcrum portion engageable with a portion of the bracket body and an acting portion engageable with a rear end portion of the base side portion, wherein the portion of the bracket body is used as a fulcrum and an engaging end portion of the rear end portion is used as a point of application. Hence, when, for example, the operation of opening the locking member (the operation of opening the slot) is effected, it is possible to apply a force for sliding the locking member while holding down the bracket body with one tool, thereby making it possible to effect the sliding operation smoothly.
In addition, if the tool for an orthodontic bracket is arranged such that the fulcrum portion is arranged to be engageable with a recessed portion in an upper end surface of the rib, the portion located in the central region of the bracket body and having sufficient strength can be used as the fulcrum portion for applying the operating force.